Have been using vSphere extensively over the years and we finally started using vCenter to manage all the hosts. I am happy but not excited, not because it is bad but I just don't feel the craftsmanship.
I use a lot of tools at work and I picked what to use all with a reason. Lately, I spend a lot of time in configuration management and Puppet is what I am using. A similar offering by VMWare is the Orchestrator.
With both tools on hand, why would I prefer learning Puppet than Orchestrator? Probably comes down to,
I am not confining myself to a particular stack of technology, I can use Puppet to manage instance virtualizing on whatever platform.
I can pick up a lot of resources on this tool since this is so common.
Best of breed
Puppet focus on what it do best and rely on (or people find a way to) other tools to fulfill the other needs. For instance, we are using GIT to manage all the .pp files versioning, access control by PKI, etc. While for Orchestrator, it is taking care all by itself. If vSphere is the only tools we use, this will not be a problem but we are not.
By the same token, this explain why I would use New Relic, Zabbix, Jenkins and Nexus instead of vFabric.